DESCRIPTION

The
kvm_dpcpu_setcpu(),
kvm_getmaxcpu(), and
kvm_getpcpu() functions are used to access the per-CPU data of active processors in the kernel indicated by
kd. Per-CPU storage comes in two flavours: data stored directly in a
struct pcpu associated with each CPU, and dynamic per-CPU storage (DPCPU), in which a single kernel symbol refers to different data depending on what CPU it is accessed from.

The kvm_getmaxcpu() function returns the maximum number of CPUs supported by the kernel.

The kvm_getncpus() function returns the current number of CPUs in the kernel.

The kvm_getpcpu() function returns a buffer holding the per-CPU data for a single CPU. This buffer is described by the struct pcpu type. The caller is responsible for releasing the buffer via a call to free(3) when it is no longer needed. If cpu is not active, then NULL is returned instead.

The kvm_read_zpcpu() function is used to obtain private per-CPU copy from a UMA_ZONE_PCPUzone(9). It takes base argument as base address of an allocation and copyies size bytes into buf from the part of allocation that is private to cpu.

The kvm_counter_u64_fetch() function fetches value of a counter(9) pointed by base address.

Symbols for dynamic per-CPU data are accessed via kvm_nlist(3) as with other symbols. libkvm maintains a notion of the "current CPU", set by kvm_dpcpu_setcpu, which defaults to 0. Once another CPU is selected, kvm_nlist(3) will return pointers to that data on the appropriate CPU.

CACHING

kvm_getmaxcpu() and
kvm_getpcpu() cache the nlist values for various kernel variables which are reused in successive calls. You may call either function with
kd set to
NULL to clear this cache.

RETURN VALUES

On success, the
kvm_getmaxcpu() function returns the maximum number of CPUs supported by the kernel. If an error occurs, it returns -1 instead.

On success, the kvm_getpcpu() function returns a pointer to an allocated buffer or NULL. If an error occurs, it returns -1 instead.

On success, the kvm_dpcpu_setcpu() call returns 0; if an error occurs, it returns -1 instead.

On success, the kvm_read_zpcpu() function returns number of bytes copied. If an error occurs, it returns -1 instead.

If any function encounters an error, then an error message may be retrieved via kvm_geterr(3).